A few times though when I pressed the shutter button to acquire and start tracking, the camera did nothing. It didn't drive the lens or even attempt to acquire focus. I released the button and tried again and it worked.
Anyone else experience a delay or refusal to acquire focus?
I experienced this same problem yesterday while trying to determine the proper MFA for my 2x extender on my 400DO (center focus point only, one shot mode). The camera did nothing a time or two and then operated normally, disconcerting to say the least. Did not happen today, not sure what is the cause.